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3phase PWM variable speed motor

Discussion in 'Electronic Basics' started by ~Dude17~, Sep 11, 2004.

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  1. ~Dude17~

    ~Dude17~ Guest

    X-No-Archive: Yes

    I took apart a DVD-ROM drive for the heck of it and the control LSI is
    amazing stuff.

    The driver chip has everything to directly drive all the mechanical
    parts in a CD-ROM drive from loading tray, focus, tracking, sled and
    the spindle motor. I find the spindle motor control the most
    fascinating.

    http://www.rohm.com/products/databook/optdisc/pdf/bd7902cfs.pdf

    The chip controls the spindle motor using three phase PWM and reading
    the controller documentation leads me to believe the thing can be
    controlled somehow with pin 24.

    The range is rather wide 230RPM while playing back audio CD at outer
    diameter and about 10,000RPM at 48x CAV mode. The chip can also apply
    reverse torque to quickly bring the disc to stop.

    Is it difficult to make a variable speed drive using the spindle motor
    and the LSI pulled from a DVD-ROm drive to let me run the motor
    anywhere from 280 to 10,000RPM outside of the original drive? It
    would surely make a cool project part.


    If this sophisticated control can be built into a $20 DVD-ROM drive,
    how expensive would it be to integrate a similar controller with
    beefier drive circuit to drive a motor in few hundred watt to a few
    kilowatt range?
     
  2. You are in the 19th century.The germans have used this since 1990.The ICE
    train (InterCityExpress) has 13,000 HP, probably 8 traction motors and 2
    "locomotives" (see www.db.de if you can read german).The motors are
    asynchronous, three-phase squirrel cage and of course they must have
    sufficient torque to pull the train at stop and enough rpm to reach the
    maximum speed of 200 km/h.The cetenary system is 15 kV 16 2/3 Hz.Of course,
    there's such a drive as in the DVD.In normal electric locomotives there's a
    motor with brushes and excitation in series (like the one your drill has or
    your mixer, the one you make the ice-cream) and a transformer with 18
    taps.To start the train, you need high current and low voltage.For maximum
    speed, you need high voltage and sufficient current.These motors are
    directly coupled on the wheels.
     
  3. Tom Grayson

    Tom Grayson Guest

    The major player in answering this question is "volume"
    Because the manufacturer can expect to sell millions of thses things,( DVD
    rom Drives) The development cost can be split, a few dollars over each item
    with no major impact in the overall price. After the development costs have
    been covered the manufacturer can then turn a reasonable profit before
    market saturation.

    Not so with larger drives. The thing is there are a lot more "Players" in
    the motor drive market and in reality, if a maunfacturer goes to market with
    say a 2KW Drive there are probably more then 30 manufacturers out there each
    trying for their share of a rather limited market, so the prospective sales
    will be maybe only in the 1,000's and not the millions that the DVD rom
    makers have at their disposal.

    another factor is PC users tend to have a rather "Geeky" approach to their
    equipment, with a fair market wanting the Latest and greatest, So they would
    be perfectily willing to throw away a perfectly good "Widgett" to replace it
    with another widgett of similar cost but more functions or better
    specifications. Usually in the industrial drive market, once a device is up
    and running, There it stays until it breaks or the whole machine is ready
    for an upgrade.

    The other thing is the DVD Rom Drives are a dedicated application, Known
    Supply Voltage, Known load inertia, One job description. as we all know
    the application of Variable speed AC Drives has about as many diferent jobs
    and supply voltages as you immagination can put together. any reputable
    drive maker must design his drive to be as adaptible as possible so that it
    can be applied to any of these aapplications. This all adds Cost to the
    development.

    Having said that, there, is no reason why the cost of drives will not fall
    as time progresses, as we learn how to do things more cost effectively and
    new technology either takes away some of the obsticales or makes them easier
    to contend with.

    Well there's my 2cents worth.
     
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